Local anesthetics potently block a potential insensitive potassium channel in myelinated nerve

Peribulbar anaesthesia for cataract surgery: prilocaine versus lignocaine and bupivacaine

PURPOSE

Prilocaine has recently been introduced for use in ocular local anaesthesia. A prospective randomised double-masked study was undertaken to assess the efficacy of prilocaine 2% plain versus a mixture of lignocaine 1% and bupivacaine 0.5%, each with hyaluronidase.

METHODS

Seventy-five patients were recruited. Local anaesthetic was given by a two-injection transconjunctival peribulbar technique. Injection and perioperative pain were graded by visual analogue pain score (range 0-10). Akinesia and orbicularis function were graded by the surgeon.

RESULTS

The two anaesthetic mixtures were comparable in efficacy in producing anaesthesia and akinesia. Using the Mann-Whitney U-test for significance, pain of injection ranked as a mean of 0.88 for prilocaine and 1.03 for lignocaine and bupivacaine (p = 0.48, U = 635.5) Perioperative pain was ranked as a mean of 1.17 for prilocaine and 0.91 for lignocaine and bupivacaine (p = 0.41, U = 629.0).

CONCLUSIONS

Prilocaine is a useful alternative anaesthetic agent for eye surgery that has low toxicity and is effective without adrenaline.

ATP-dependent potassium channel in rat cardiomyocytes is blocked by lidocaine. Possible impact on the antiarrhythmic action of lidocaine

BACKGROUND

During myocardial ischemia, lidocaine has favorable antiarrhythmic properties. Malignant arrhythmias result from heterogeneity between ischemic and nonischemic regions in extracellular potassium concentration and action potential duration. These effects have been attributed to the activation of ATP-dependent potassium (KATP) channels. In this study, we investigated the action of lidocaine on the KATP channels to test the possible link between the antiarrhythmic properties of lidocaine and its action on the KATP channel.

METHODS AND RESULTS

The patch-clamp technique was employed on enzymatic dissociated cardiomyocytes of adult rats. Lidocaine was applied to the outer side of excised membrane patches by means of a multibarrel perfusion system. Lidocaine reversibly blocked the mean current of the KATP channels in a concentration-dependent manner (IC50 = 43 +/- 4.7 mumol/L, E = 0 mV, n = 6), while the amplitude of the single-channel current remained unchanged. The half-maximum blocking concentration corresponds to the therapeutic range for the antiarrhythmic application of a lidocaine bolus in humans.

CONCLUSIONS

The open probability but not the conductance of the KATP channel in the membrane of rat cardiomyocytes is blocked by lidocaine. This action may explain, in part, the favorable antiarrhythmic properties of lidocaine during acute myocardial ischemia.

Alcohols inhibit a cloned potassium channel at a discrete saturable site. Insights into the molecular basis of general anesthesia

The molecular basis of general anesthetic action on membrane proteins that control ion transport is not yet understood. In a previous report (Covarrubias, M., and Rubin, E. (1993) Proc. Natl. Acad. Sci. 90, 6957-6960), we found that low concentrations of ethanol (17-170mM) selectively inhibited a noninactivating cloned K+ channel encoded by Drosophila Shaw2. Here, we have conducted equilibrium dos-inhibition experiments, single channel recording, and mutagenesis in vitro to study the mechanism underlying the inhibition of Shaw2K+ channels by a homologous series of n-alkanols (ethanol to 1-hexanol). The results showed that: (i) these alcohols inhibited Shaw2 whole-cell currents, the equilibrium dose-inhibition relations were hyperbolic, and competition experiments revealed the presence of a discrete site of action, possibly a hydrophobic pocket; (ii) this pocket may be part of the protein because n-alkanol sensitivity can be transferred to novel hybrid K+ channels composed of Shaw2 subunits and homologous ethanol-insensitive subunits: (iii) moreover, a hydrophobic point mutation within a cytoplasmic loop of an ethanol-insensitive K+ channel (human Kv3.4) was sufficient to allow significant inhibition by n-alkanols, with a dose-inhibition relation that closely resembled that of wildtype Shaw2 channels; and (iv) 1-butanol selectively inhibited long duration single channel openings in a manner consistent with a direct effect on channel gating. These results strongly suggest that a discrete site within the ion channel protein is the primary locus of alcohol and general anesthetic action.